VF - Horopter - Week 3 Flashcards
Define corresponding points.
Retinal elements that give rise to the same visual direction. One is it temporal, the other is nasal.
Define disparate points.
Non-corresponding points that give rise to different visual directions.
Describe the theoretical point horopter.
Locus of all points in real visual space that are immaged onto corresponding points. As a result, no diplopia occurs.
Describe the Veith-Muller circle. What 3 assumptions does it make.
A theoretical horopter that is based on the assumption that angular symmetry of corresponding points exist.
It also assumes that the eyes are spherical, and that the centre of rotation of the eye, its nodal point, and the geometric centre of the eye are coincident.
Name the 5 methods of measuring the horopter.
Nonius method Haplopic method Apparent fronto-parallel plane method Minimum stereo-threshold method Zero vergence method
Describe the Nonius method. Describe what each eye sees.
Subject looks through two screens, with four quadrants.
The inner bottom quadrant is empty.
The outer bottom, and and inner top quadrants are occluding. The outer top quadrants are slits.
The subject fixates on a target in the middle of the background.
A test rod is present to the right.
The right eye will see the top half of the test rod discontinuously.
The left eye will see the bottom half of the test rod continuously.
The two rods are not always aligned, and the rod can be moved in depth by the subject until they are aligned. The position of the test rod when aligned is in line with the horopter.
Describe the haplopic method.
All objects on the horopter are seen singly with no diplopia.
When too far or too near, they become diplopic, and are out of the horopter.
A series of rods whose depths can be changed are placed on either side in series of a focus target rod.
The depths at which crossed and uncrossed diplopia occur are measured.
Describe the apparent fronto-parallel plane method.
A series of rods at the same depth are presented to a subject.
The subject will perceive them to be curving away from them.
They are asked to adjust the rods until they have the same depth.
In reality, the rods will now be curving inwards.
Which method is the most precise and reliable? What is a problem with it?
Apparent fronto-parallel plane method.
Its rationale is the most indirect however.
Which method has the most direct rationale? What is a problem with it?
Nonius method.
Doesnt actually involve binocular vision however.
What is a disadvantage of the haplopic method?
Yields a solid horopter,rather than a locus of points.
Define panums area.
The concept that the horopter isnt a single line, but an area that relies on a threshold phenomena.
Define the Hering-Hillebrand horopter deviation, and how it can be explained.
The empirical horopter at 40cm is platter than the VM circle, the deviation is the area between.
Can be explained by the fact that angluar symmetry doesnt hold.
How can horopters be skewed?
If there is unequal magnification due to high power between the eyes, it can skew the horopter and result in flat surfaces appearing tilted or curved.
